High speed printers and copiers such as those made and sold by Heidelberg Digital, assignee of this patent, use a biased transfer roller to transfer toner or developing material from a developed image on a photo conductor or equivalent film to a receiver sheet. The transfer roller is electrostatically biased to transfer charged toner particles from the surface of the photo conductor or equivalent film to a receiver sheet such as paper. During a normal operation residual toner on the photo conductor or equivalent film attaches to the surface of the transfer roller. To prevent that residual toner from transferring to the back surface of the following receiver sheet, an acrylic fiber brush rotates, engages the surface of the transfer roller, and removes residual toner particles. The toner on the bush is carried past a vacuum cleaning station that removes the toner and deposits it in a waste receptacle.
High speed printers and copiers may generate in excess of 100 copies per minute. In one day they can generate thousands of copies. The residual toner particles may accumulate on the transfer roller and cause unwanted markings on copies. Often such unwanted markings are not detected until after a large print job is completed. Such unwanted markings are unacceptable and many large print and copy jobs must be redone. The unwanted markings cause a waste of paper that is costly to the user, is inefficient, and adversely impacts wood and paper resources. The transfer roller may have to be manually cleaned. That reduces the productivity of the copier/printer and adds unwanted maintenance costs to the user of the copier/printer. Because the transfer roller is driven by the photo conductor or equivalent film or a drum, it is conventional to set the engagement between the transfer roller and the cleaning brush to avoid slipping or stalling the transfer roller. A stalled transfer roller will smear copies and likewise ruin a large print job. Accordingly, there has long been an unmet need to improve cleaning of transfer rollers in high speed copiers and printers without stalling the transfer roller.
The invention improves the transfer roller cleaning operation in copiers and printers. It provides design criteria for selecting the engagement between the transfer roller and the cleaning brush. The criteria include selecting an engagement distance for pressing together the transfer roller and cleaning brush without slipping or stalling the transfer roller and smearing the receiver sheet with toner. The criteria include selecting a fiber density for the cleaning brush from a range of densities in accordance with the engagement force between the rollers. By using the invention those who are skilled can improve the cleaning performance of copiers and printers. As a result, there are fewer ruined print jobs and less downtime for cleaning transfer rollers.
One feature of the invention is a method for adjusting a transfer roller cleaning station to provide efficient and improved cleaning of the transfer roller. The transfer roller is frictionally driven by an endless belt photo conductor or equivalent film or a drum. That film carries a developed image past the transfer roller where the image is transferred to a receiver sheet. A cleaning station removes residual toner particles from the transfer roller. The cleaning station includes a cleaning brush with a plurality of fibrous bristles that extend from the cleaning brush toward the transfer roller. The force of the bristles against the transfer surface is adjusted by moving the cleaning brush toward the transfer roller. Once the desired engagement is selected, the cleaning brush is locked into position and maintains a relatively constant engagement on the transfer roller. The cleaning brush is driven by its own motor in a direction opposite to the direction of the transfer roller.
Conventional means are used for determining stall torque for slowing or stopping the rotation of the transfer roller. The cleaning brush is moved to engage its bristles against the transfer roller with an initial force that is sufficient to deflect the bristles against the transfer roller and begin removing at least some residual developing material from the transfer roller. The cleaning brush is moved in small, incremental steps toward closer engagement with the transfer roller. At each step, the performance of the cleaning of the transfer roller is recorded. The cleaning performance improves little or none until a first engagement threshold is exceeded. Thereafter, cleaning performance continuously improves until the stall torque is reached. Cleaning performance also improves as the density of the fibrous bristles on the cleaning brush increases. Thus, cleaning performance below the stall torque is improved by increasing the engagement force and by increasing the density of the bristles in the cleaning brush.